This invention relates to a photosensitive device, especially a photosensitive device capable of high voltage operation.
Photosensitive devices have been proposed which include a semiconductor body having a first region of one conductivity type adjacent a given surface of the body, a second region of the opposite conductivity type surrounding the first region so as to form with the first region a photosensitive main pn junction, means for transmitting light into the semiconductor body via the given surface to enable photogeneration of charge carriers in the vicinity of the photosensitive main pn junction and a further region, of the one conductivity type surrounding the photosensitive main pn junction to form a pn junction with the second region, the further region lying within the spread of the depletion region of the photosensitive main pn junction when the photosensitive main pn junction is reverse-biassed in operation of the device, so as to increase the breakdown voltage of the photosensitive main pn junction.
GB-A-1,357,432 describes such a photosensitive device. In particular, GB-A-1,357,432 describes a photosensitive diode in which the photosensitive main pn junction is surrounded by a guard ring which meets the given surface and is spaced apart from the photosensitive main pn junction forming a pn junction with the second region. The guard ring serves to reduce leakage currents and to increase the breakdown voltage of the photosensitive main pn junction. As described in the specification, in addition to the required diode terminals, a contact is provided on the guard ring. The photosensitive junction is essentially provided between a large-area shallow light collecting subsidiary region of the first region and the second region, contact metallization being provided on a deeper subsidiary region of the first region surrounding the light collecting subsidiary region. Should a photosensitive transistor be required, then an annular emitter region can be provided within the first region so as to be within the deeper subsidiary regions of the first region which forms the base of the transistor, contact metallization being provided on the surface of the emitter region.
In order to increase further the breakdown voltage of the photosensitive main pn junction, additional guard rings, for example floating rings or another high voltage edge termination system, may be provided around the photosensitive main pn junction. However, as the desired breakdown voltage becomes higher, the area of the device consumed by the edge termination system comes to dominate the device area and may result in the active area available for light collection or amplification having to be reduced.